Fix rectifier effect description

gui/index.html

 <script type="text/x-red" data-help-name="AudioEffectRectifier">
 	<h3>Summary</h3>
 	<div class=tooltipinfo>
-	<p>Pass only the positive portion of a waveform
+	<p>Invert the negative portion of a signal, similar to a full wave rectifier circuit.
 	</p>
 	</div>
 	<h3>Audio Connections</h3>
 	<h3>Functions</h3>
 	<p>There are no functions to call from the Arduino sketch.
 		This object simply passes the positive portion of the
-		signal and outputs zero when the input is negative.
+		signal and inverts the signal when the input is negative.
 	</p>
 <h3>Examples</h3>
 	<p class=exam>File &gt; Examples &gt; Audio &gt; Effects &gt; Vocoder19Band